HomeMy WebLinkAboutGoodnews Bay Wind Project Mini Conceptual Design Report - May 2023 - REF Grant 7013002Photo Credit: Northern Power Systems
Photo Credit: V3 Energy, LLC / Google Earth
Goodnews Bay Wind Resource
Assessment Report
Goodnews Bay, AEA photo
June 13, 2022
Douglas Vaught, P.E.
V3 Energy, LLC
Anchorage, Alaska
www.v3energy.com
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Contents
Introduction..................................................................................................................................................1
Met Tower Location and Data Summary......................................................................................................1
Data Quality and Synthesis.......................................................................................................................2
Wind Speed...............................................................................................................................................3
Wind Direction..........................................................................................................................................4
Temperature and Density.....................................................................................................................5
IEC Classification...........................................................................................................................................5
Extreme Wind...........................................................................................................................................6
Goodnews Bay Met Tower Site.............................................................................................................6
Turbulence Intensity.................................................................................................................................6
Goodnews Bay Met Tower Site.............................................................................................................7
Wind Shear................................................................................................................................................7
Goodnews Bay Met Tower Site.............................................................................................................7
Wake Turbulence......................................................................................................................................8
Goodnews Bay Met Tower Site.............................................................................................................8
Flow Inclination.........................................................................................................................................8
Goodnews Bay Met Tower Site.............................................................................................................8
Wind Distribution......................................................................................................................................8
Goodnews Bay Met Tower Site.............................................................................................................8
Met Tower Site IEC 61400-1 Classification...............................................................................................9
Wind Flow Modeling.....................................................................................................................................9
Goodnews Bay WAsP Model.....................................................................................................................9
Global Wind Atlas........................................................................................................................................11
Conclusion and Recommendations ............................................................................................................11
Met Tower Documentation Photos............................................................................................................12
Figure 1: Goodnews Bay met tower location, Google Earth image, view to northeast...............................1
Figure 2: Sensor icing events time graph......................................................................................................2
Figure 3: Automatic detection of tower shadow with paired 34-meter level anemometers......................3
Figure 4: Tower shadow time graph.............................................................................................................3
Figure 5: Met tower wind rose ......................................................................................................................4
Figure 6: Platinum Airport wind rose ............................................................................................................4
Figure 7: Temperature boxplot.....................................................................................................................5
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Figure 8: Air density boxplot.........................................................................................................................5
Figure 9: Met tower site wind shear profile.................................................................................................8
Figure 10: Wind speed distribution, or histogram........................................................................................9
Figure 11: WAsP software resource grid of wind speed, hill area north of Goodnews Bay.......................10
Figure 12: Google Earth image of WAsP wind speed resource grid export................................................10
Figure 13: Global Wind Atlas data describing met tower site and surrounding ridge ...............................11
Figure 14: Goodnews Bay met tower, view west, AEA photo .....................................................................12
Figure 15: Goodnews Bay me tower base, view north, AEA photo............................................................13
Figure 16: Goodnews Bay met tower base, view east, AEA photo.............................................................13
Figure 17: Goodnews Bay met tower base, view south, AEA photo..........................................................14
Figure 18: Goodnews Bay met tower base, view west, AEA photo............................................................14
Table 1: Met tower site data.........................................................................................................................2
Table 2: Goodnews Bay met tower data channels.......................................................................................2
Table 3: Wind speed summary .....................................................................................................................4
Table 4: IEC 61400-1, 3rd edition, simplified wind classification...................................................................6
Table 5: IEC 61400-1, 3rd edition, extreme wind classes ..............................................................................6
Table 6: Calculated extreme wind probability..............................................................................................6
Table 7: IEC 61400-1, 3rd edition, turbulence categories..............................................................................7
Table 8: Turbulence intensity........................................................................................................................7
Table 9: WAsP-predicted wind speeds at selected locations.....................................................................10
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Introduction
V3 Energy LLC was contracted by Alaska Village Electric Cooperative, Inc. (AVEC) to prepare a wind
resource assessment report for the village of Goodnews Bay, one of its member communities. Wind
data was collected from August 2015 to May 2016 from a meteorological (met) test tower installed by
Alaska Energy Authority (AEA). Analysis of this data, though representing less than one full year’s worth,
indicates a robust Class 5 to Class 6 wind resource with characteristics suitable for the development of
wind power.
Met Tower Location and Data Summary
Per correspondence provided to V3 Energy by AEA, AEA installed a 34-meter height met tower on a
ridge immediately north of the Goodnews Bay village center (see Figure 1) in mid-December 2014 with
assistance from local personnel. Unfortunately, the datalogger was inadvertently discarded during the
installation process and not replaced until the following August. The met tower operated normally from
that point until it reportedly collapsed for unknown reasons in May 2016, hence less than 12 months of
data were collected.
Figure 1: Goodnews Bay met tower location, Google Earth image, view to northeast
Written documentation of the installation was not provided to V3 Energy, but sensor and other
information were attained from several photographs forwarded to V3 Energy and from metadata
embedded in the data files (refer to Table 1 and Table 2).
Met tower
Goodnews Bay
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Table 1: Met tower site data
Site number 4663
Installation date 20 December 2014
Data start date 12 August 2015
Data end date 12 May 2016
Tower and logger NRG 34-meter, NRG Symphonie Pro
Site latitude/longitude and elevation 59.1284, -161.5775; 104 meters (342 ft.)
Time Zone Alaska Standard Time (UTC-09:00)
Table 2: Goodnews Bay met tower data channels
Sensor Model Serial No. Height Orientation
1 Slope Offset Units
Anem. 34m A NRG 40C unknown 34 m North
2 0.765 0.350 m/s
Anem. 34m B NRG 40C unknown 34 m West 0.765 0.350 m/s
Anem. 20m NRG 40C unknown 20 m North 0.765 0.350 m/s
Direction 34 NRG 200P none 34 m East 0.351 90 deg. ° True
Temperature NRG 110S none 2 m Northeast 0.136 -86.383 Deg. C
The wind resource measured at the Goodnews Bay met tower site is excellent with a high mean wind
speed (for the nine measured months), low turbulence, low wind shear, but possibly moderately high
extreme winds (as predicted from the very short 9-month data measurement period).
Data Quality and Synthesis
Met data was reviewed and filtered for icing and other problems. In general, the data set was clean with
fully functional sensors throughout the 9 months data period. Icing was manually flagged when
temperature < 0° C, sensor standard deviation = 0, speed = 0 or direction “frozen”, and sensor return
exhibited a characteristic loss and restart of normal data indicative of typical icing events. Icing was
moderate with approximately 4% data loss and confined to the coldest months of November through
March (see Figure 2).
Figure 2: Sensor icing events time graph
Further filtering was employed to detect tower shadow of the paired 34-meter anemometers. This
occurs when a sensor is inside a 30° cone opposite the measured wind direction (see Figure 3).
Windographer wind analysis software (used for this analysis) automatically flags this data for removal
(see Figure 4).
Post flagging data processing was accomplished to reconstruct the data set with the non-obstructed
data points for tower shadow and synthesized data for icing events. The latter employs a statistical
1 Determined from photos provided to V3 Energy by AEA
2 Presumed as a typical wiring arrangement
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method to reconstruct most probable wind behavior during the periods when icing prevented sensor
function.
Finally, the paired 34-meter level anemometers were mathematically combined by Windographer
software into a single representative 34-meter anemometer to best represent wind conditions at that
level.
Figure 3: Automatic detection of tower shadow with paired 34-meter level anemometers
Figure 4: Tower shadow time graph
Wind Speed
Anemometer data obtained from the met tower, from the perspectives of both mean wind speed and
mean wind power density, indicate a very strong wind resource. Note that cold temperatures
contributed to a higher wind power density than standard conditions would yield for the measured
mean wind speeds. This is reflected in the cubed root mean cubed (CRMC) wind speed, which reflects a
calculation of a steady wind speed, at the measured mean air density, that would yield the measured
mean wind power density. In other words, the winds punch above their weight. But bear in mind that
this data represents only nine months, with summer missing. Inclusion of summer data would decrease
the mean wind speed and with a higher mean temperature (and hence lower density) lessen the spread
between the mean and CRMC wind speeds.
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Table 3: Wind speed summary
Variable
Speed 34m
A
Speed 34m
B
Speed 34m
cmb
Speed
20m
Measurement height (m) 34 34 34 20
Mean wind speed (m/s) 7.76 7.65 7.70 7.30
Max 10-min wind speed (m/s) 34.6 34.4 34.5 33.4
Max gust wind speed (m/s) 41.3 40.9 n/a 40.5
CRMC wind speed (m/s) 10.3 10.2 10.2 9.7
Weibull k 1.69 1.67 1.68 1.68
Weibull A (m/s) 8.69 8.56 8.63 8.18
Mean power density (W/m²) 684 662 673 573
Energy pattern factor 2.32 2.34 2.33 2.33
Frequency of calms (%)3 24.6 25.0 24.7 25.7
Diurnally, the winds are strongest mid-afternoon and weakest early morning, as one would expect.
Desirably for wind power, this coincides with a typical electric load demand profile.
Wind Direction
Wind direction measured by the met tower indicates predominately northwest winds (see Figure 5). This
is mostly confirmed by the Platinum Airport Automated Weather Observing Station (AWOS)4 located
about 11 miles to the southwest, which indicates north-northwesterly and southeasterly winds (see
Figure 6). Possibly a direction offset error was keyed into the datalogger, but AEA’s installation
documentation photos show the sensor facing east and the logger offset was programmed to 090
degrees, so the met tower direction data is presumed accurate.
Figure 5: Met tower wind rose Figure 6: Platinum Airport wind rose
3 Percent time wind speeds < 4 m/s
4 Goodnews Bay Airport is not equipped with an AWOS
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Temperature and Density
A mean temperatue of 2.3° C was measured at the met tower site, but the data period excludes
summer, so true annual temperature is substantially higher (see Figure 7). By the same measure, the
calculated air density of 1.265 kg/m3 is higher than would be true with inclusion of summer data (see
Figure 8)5.
Figure 7: Temperature boxplot
Figure 8: Air density boxplot
IEC Classification
Six parameters or analyses comprise IEC 61400-1 wind classification as listed below, with the simplified
classification comprising only extreme wind probability and turbulence intensity (see Table 4). They are:
Extreme wind
Turbulence intensity
Wind shear
Wake turbulence
Flow inclination
Wind distribution
5 Note standard air temperature of 14.3° C and standard air density of 1.213 kg/m
3 at 100 m elevation
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Table 4: IEC 61400-1, 3rd edition, simplified wind classification
Wind Class I II III S
Vref (m/s) 50.0 42.5 37.5 Values specified
by the designerA (TIref) 0.16
B (TIref)0.14
C (TIref) 0.12
Extreme Wind
The classification of extreme wind is by Vref, the reference wind speed; the highest measured or
probable 10-minute average wind speed in a 50-year return period. This can be accomplished with a
periodic maxima analysis (by Gumbel distribution), the method of independent storms (also a Gumbel
distribution), and European Wind Turbine Standards II (EWTS II).6
Table 5 includes Vref as presented in Table 4, plus Ve50, the maximum measured or probable 3-second
average or gust wind speed in a 50-year return period. Ve50 is defined as Vref x 1.4 (for equivalent height),
though the latter is not part of the IEC 61400-1, 3rd edition simplified classification noted in Table 4.
Table 5: IEC 61400-1, 3rd edition, extreme wind classes
Wind Class I II III S
Vref (m/s) 50.0 42.5 37.5 Designer spec.
Ve50 (m/s) 70.0 59.5 52.5
Goodnews Bay Met Tower Site
Nine months of data are too few to estimate extreme wind probability with confidence, but results are
presented as a guide to possible expected site conditions. Note that periodic maxima, method of
independent storms, and Ve50 by any method cannot be calculated with less than 12 months of data. But
by EWTS II Goodnews Bay extreme wind probability appears to be moderately high, classifying as IEC
61400-1, 3rd ed. Wind Class I or II at the 34 m level (see Table 6).
Table 6: Calculated extreme wind probability
Turbulence Intensity
The turbulence intensity (TI) is a dimensionless number defined by the standard deviation () of the
wind speed within each time step (10 minutes for wind power analysis) divided by the mean wind speed
(V) over that time step (see Equation 1).
6 EWTS II does not consider peak winds, rather only mean wind speed and Weibull k value.
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Equation 1: Turbulence intensity
=
IEC 61400-1, 3rd ed., defined turbulence categories based on mean turbulence intensity at a wind speed
of 15 m/s (see Table 7).
Table 7: IEC 61400-1, 3rd edition, turbulence categories
Turb. Category S A B C
TI at 15 m/s >0.16 0.14-0.16 0.12-0.14 <0.12
Goodnews Bay Met Tower Site
Turbulence calculated from the met tower anemometers indicate very smooth air with TI well the
Category C threshold (see Table 8).
Table 8: Turbulence intensity
Wind Shear
A wind shear, or power law, exponent is calculated by Equation 2 where V = wind speed and Z = height
above ground level. =0 would indicate no wind shear and =0.2 would indicate very high wind shear.
Equation 2: Wind shear
()=() ×
Goodnews Bay Met Tower Site
Met tower anemometer data indicates a power law exponent () of 0.115, which is relatively low (0.14
is considered nominal in the wind power industry) and reflective of excellent wind shear characteristics
for wind turbine operations (see Figure 9).
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Figure 9: Met tower site wind shear profile
Wake Turbulence
In comparison to the normal turbulence model, IEC 61400-1 suggests an effective turbulence intensity,
which is an ideal turbulence independent of wind direction and expected to cause the same fatigue
damage as variable turbulence in winds from all directions. The effective turbulence intensity includes
turbulence from wakes of neighboring turbines.
7
Goodnews Bay Met Tower Site
Given the highly directional nature of the wind rose – noting that summer data is not included – wake
turbulence should be minimal with careful placement of multiple wind turbines in a line perpendicular
to the prevailing wind.
Flow Inclination
A wind flow vector not exceeding 8 degrees from horizontal (plus or minus).
Goodnews Bay Met Tower Site
The met tower was not equipped with a vertical wind flow sensor, hence flow inclination cannot be
calculated. Given that the met tower was located on a ridge with lower elevation terrain to the west
(towards the bay), moderate wind flow inclination should be expected.
Wind Distribution
A wind speed, or histogram, where a Weibull function 8 yields a unitless shape factor (k) of 2.0 (known as
a Rayleigh distribution) or less.
Goodnews Bay Met Tower Site
Data from the 34-meter combined anemometer yields a wind speed distribution with Weibull k value of
1.57, which is slightly lower than ideal, indicating a moderate predominance of calm winds. Interestingly
though, winds between 9 and 14 m/s are over-represented compared to ideal Weibull curves (refer to
Figure 10). Note that summer data is not represented.
7 The IEC 61400-1 turbine safety standard - WAsP
8 Weibull distribution - Wikipedia
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Figure 10: Wind speed distribution, or histogram
Met Tower Site IEC 61400-1 Classification
Per the simplified IEC 61400-1, 3rd edition classification and noting the paucity of data for extreme wind
probability calculations, the met tower site classifies as likely Class IIC or very low Class IC. Per the
expanded classification criteria, no disqualifying wind behavior is noted in the data set.
Wind Flow Modeling
WAsP (Wind Atlas Analysis and Application Program) is a PC-based software designed to estimate wind
resource and power production for individual wind turbines and/or wind turbine farms.
WAsP modeling begins with import of a digital elevation map (DEM) of the subject site and surrounding
area and conversion of coordinates to Universal Transverse Mercator (UTM). UTM is a geographic
information system that uses two-dimensional Cartesian coordinates to identify locations on the surface
of Earth. UTM coordinates reference the meridian of its zone with 60 longitudinal zones for the easting
coordinate and 20 latitude bands for the northing coordinate. Easting and northing units are meters and
elevations of the DEMs are converted to meters if necessary for import into WAsP software.
A met tower reference point is added to the digital elevation map, wind turbine locations identified, and
a wind turbine model selected to perform the calculations. WAsP considers the orographic (terrain)
effects on the wind, plus surface roughness variability and obstacles if added, and calculates wind speed
increase or decrease at each node of the DEM grid. The mathematical model, although robust, has
several limitations, including an assumption that the wind flow regime at the turbine site is like that at
the met tower reference site, prevailing weather conditions are stable over time, and the surrounding
terrain is sufficiently gentle and smooth to ensure laminar, attached wind flow.
Goodnews Bay WAsP Model
A one-third arc second high-resolution digital elevation map of Goodnews Bay was downloaded from
USGS’ National Elevation Database and converted to UTM before processing for use with WAsP
software. A resource grid was defined to visually display selected data, such as wind speed, across an
area of interest (see Figure 11). From it, comparative wind speeds relative to the met tower reference
point can be calculated (refer to Table 9).
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Figure 11: WAsP software resource grid of wind speed, hill area north of Goodnews Bay
Table 9: WAsP-predicted wind speeds at selected locations
Note that WAsP software predicts a higher wind speed at the met tower site than was measured (7.95
m/s vs. 7.70 m/s). This relates to the conversion methodology of WAsP software. Note too that either
speed only represent nine months of data with the lower wind speeds of summer months not included.
The WAsP software resource grid can be exported to Google Earth for visualization and to aid project
planning efforts (see Figure 12).
Figure 12: Google Earth image of WAsP wind speed resource grid export
1
2
3
2
31
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Global Wind Atlas
With less than a full year of wind data, true mean speed at the met tower site is uncertain. While not
necessarily problematic for IEC 61400-1 classification, estimated wind turbine annual energy production
will also be uncertain. An option then is to assess the site using one or more global wind models. One is
Global Wind Atlas.9 Selecting a small area at the 50-meter level that encompasses the met tower site
and the surrounding ridge, Global Wind Atlas predicts a mean annual wind speed of 7.85 m/s and a wind
rose more like that reported from the Platinum Airport AWOS than the Goodnews Bay met tower (see
Figure 13. The mean wind speed correlates well with wind speed data collected from the met tower, but
the wind rose discrepancy is not obvious. For installation of only one or two wind turbines, this would be
a moot point as the discrepancy can be accommodated.
Figure 13: Global Wind Atlas data describing met tower site and surrounding ridge
Conclusion and Recommendations
The wind data collected at the met tower site in Goodnews Bay is shorter than standard (nine months
vs. normal 12 months minimum), but it’s sufficient to characterize the site by IEC 61400-1, 3rd edition as
Class IIC, which enables one to select a suitable wind turbine. Caution should be exercised though in
predicting wind turbine annual energy production as the nine months of data exclude the typically low
wind summer months. Wind resource software such as Global Wind Atlas can lessen this risk though and
enable development of a wind power project.
9 Global Wind Atlas is a joint initiative of Technical University of Denmark (DTU) and the World Bank Group. Note
that DTU developed WAsP software.
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Met Tower Documentation Photos
Figure 14: Goodnews Bay met tower, view west, AEA photo
Goodnews Bay Wind Resource Assessment Report P a g e | 13
Figure 15: Goodnews Bay me tower base, view north, AEA
photo
Figure 16: Goodnews Bay met tower base, view east, AEA
photo
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Figure 17: Goodnews Bay met tower base, view south, AEA
photo
Figure 18: Goodnews Bay met tower base, view west, AEA
photo
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